HEAT. 



cate balance, until they acquired the 

 temperature of the room, 61 : he then 

 submitted them to the influence of an 

 atmosphere at 34 for twenty- four hours, 

 without effect, as the weights remained 

 precisely the same ; although it is cer- 

 tain, from the respective capacities of 

 the two fluids, that the water must have 

 given out much more heat than the 

 quicksilver. 



In making other experiments with 

 bottles containing different fluids, he 

 found that difference of temperature in 

 the bottle, when weighed, occasioned an 

 apparent difference of weight, as he 

 supposed from the vertical currents 

 which they occasioned in the atmo- 

 sphere, when heated or cooled in it ; or 

 from the unequal quantities of moisture 

 condensed upon their surfaces, or from 

 both causes operating together. 



The hypothesis, or supposition, by 

 which caloric is considered a subtile 

 material fluid, the particles of which 

 mutually repel each other, appears to 

 give a plausible explanation of most 

 of the phenomena dependant upon 

 heat, as the expansion, fusion, and 

 vaporisation of bodies, on the sup- 

 position that the particles of caloric 

 when interposed between the parti- 

 cles of bodies, in sufficient quantity, 

 produce these effects. It is natural to 

 suppose, when a body is enlarged in 

 bulk, that the enlargement is occasioned 

 by the introduction of the particles of 

 other matter, by which the particles of 

 the expanded body are repelled to a 

 greater distance from one another ; and 

 this repulsion becomes so great, in con- 

 sequence of the introduction of a large 

 quantity of heat, as to enable the par- 

 ticles of solid bodies to assume the fluid 

 or aeriform states. 



The communication of heat from one 

 body to another is also accounted for by 

 this hypothesis, on the supposition that 

 bodies have the power of attracting this 

 refined matter. According to the same 

 hypothesis, we may account for the un- 

 equal effects produced by equal quan- 

 tities of heat, upon different bodies, by 

 supposing them to exert different de- 

 grees of attraction for caloric. The 

 cold which is occasioned by the con- 

 version of solid substances into fluids 

 or gases, and the great increase of tem- 

 perature which attends the condensation 

 of s;ases or fluids, admits of satisfactory 

 elucidation upon this hypothesis, the 

 matter of heat or caloric heing ab- 

 sorbed, it is supposed, in the lormer 

 case, ancl set free in the latter* 



There are phenomena, however, which 

 are not easily reconciled to this hypo- 

 thesis ; the high degree of heat occa- 

 sioned by the explosion of gunpowder, 

 where large quantities of gaseous mat- 

 ter are disengaged ; the heat which re- 

 sults from the decomposition of euchlo- 

 rine gas, although it is resolved into 

 gases of greater volume; and the pro- 

 duction of heat by friction or percus- 

 sion. 



Dr. Murray was of opinion that there 

 is a strong analogy between the usual 

 mode of exciting electricity and the 

 production of heat by friction, and that 

 the phenomenon may be explained con- 

 sistently with the hypothesis alluded to. 



According to this author, the particles 

 of bodies are made to vibrate or oscillate 

 by friction, percussion, or other mecha- 

 nical impulse, and that during this state 

 of motion they must ultimately ap- 

 proach to and recede from each other : 

 when the particles approach, part of the 

 caloric interposed between these par- 

 ticles must be forced out ; and when 

 they recede from each other, caloric 

 must be absorbed. A part of the caloric 

 set free at every vibration is evolved ; 

 and it is supposed that its loss is sup- 

 plied by other bodies, with which the 

 body operated upon may be in contact, 

 in consequence of the strong tendency 

 of caloric to maintain an equilibrium, 

 in the same w T ay as electricity is supplied 

 to an electrical machine in action and in 

 contact with the earth. 



The caloric that is continually evolved 

 raises the temperature of the substance 

 undergoing friction, or percussion, which 

 bears some analogy to the charging of 

 an electrical conductor, with the electri- 

 city given out by the action of the elec- 

 trical machine. 



It has been proved by Berthollet that 

 there is a close connexion between the 

 heat produced by percussion, and the 

 reduction of bulk which the body ope- 

 rated upon undergoes. Pieces of gold, 

 silver, copper and iron, alike in size, 

 were submitted to the stroke of a coin- 

 ing press, by this philosopher, and the 

 heat produced by each stroke was as- 

 certained by throwing the pieces into 

 water ; the relation existing between 

 the degree of heat imparted to the 

 water, and the heat previously existing 

 in the metal, having been found by ex- 

 periment. In this manner he was ena- 

 bled to determine how much the tem- 

 perature of each piece had been raised ; 

 and the important fact resulting from 



B a 



